1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine having a first fuel injection mechanism (an in-cylinder injector) injecting fuel into a cylinder and a second fuel injection mechanism (an intake manifold injector) injecting the fuel into an intake manifold or an intake port, and particularly, to a technique wherein a fuel injection ratio between the first and second fuel injection mechanisms are considered to determine a fuel increase value in a cold state operation.
2. Description of the Background Art
An internal combustion engine having an intake manifold injector for injecting fuel into an intake manifold of the engine and an in-cylinder injector for injecting the fuel into a combustion chamber of the engine, and configured to stop fuel injection from the intake manifold injector when the engine load is lower than a preset load and to carry out fuel injection from the intake manifold injector when the engine load is higher than the set load, is known.
There is the following technique related to such an internal combustion engine. At a very low temperature, starting capability is impaired due to poor atomization of fuel. Additionally, at a very low temperature, the viscosity of a lubricating oil is high and therefore a friction increases and the number of cranking revolutions decreases. Accordingly, with a high-pressure fuel pump directly driven by an engine, a fuel pressure cannot fully be increased. A required fuel quantity may not be supplied to the engine solely with a fuel injection valve (a main fuel injection valve) provided for injecting a fuel directly into a combustion chamber, and the starting capability may further be impaired. Therefore, one proposal has been made to provide, in addition to the main fuel injection valve, a single auxiliary fuel injection valve, referred to as a cold start valve, at a collector portion upstream of an intake manifold for injecting the fuel only when the engine is started at a cold temperature (cold-start), in order to ensure a fuel quantity required at cold start that cannot be fully ensured solely with the main fuel injection valve.
A fuel supplying apparatus for an internal combustion engine of a direct-injection type disclosed in Japanese Patent Laying-Open No. 10-018884 is an apparatus for supplying fuel, which is delivered from a high-pressure pump of an engine-driven type, through direct injection into a cylinder via main fuel supplying means. The apparatus includes auxiliary fuel supplying means for supplementing a fuel supply from the main fuel supplying means at a prescribed start-up, and characterized in that a supply fuel quantity from the auxiliary fuel supplying means is estimated to correct a supply fuel quantity from the main fuel supplying means based on the estimation result.
According to the fuel supplying apparatus for an internal combustion engine of a direct-injection type, when it is necessary to actuate the auxiliary fuel supplying means (for example, when a fuel supplying pressure to the main fuel supplying means is lower than a prescribed value at cold-start), a supply fuel quantity from the auxiliary fuel supplying means is estimated, and a supply fuel quantity from the main fuel supplying means can be corrected based on the result. Accordingly, the actual supply fuel quantity to the engine can optimally be controlled to meet the supply fuel quantity required for the engine.
However, for a range shared by the in-cylinder injector and the intake manifold injector to both inject the fuel, including a transitional period from the cold state to a warm state, the cylinder's interior and the intake port increase in temperature at different rates, and therefore injected fuel deposits on the wall surface or on the top surface of the piston by different degrees. Accordingly, an accurate cold state increase value cannot be calculated if determined using only an engine coolant temperature.